Downhole formation fluid sampling tools, such as the Schlumberger Modular Formation Dynamics Tester (MDT™), withdraw samples of fluids from earth formations for subsequent analyses. These analyses are needed to characterize physical properties such as water and oil volume fractions, oil viscosity, and water salinity, among others, and are helpful in contamination monitoring. This knowledge is needed to interpret wireline well logs as well as plan for the efficient exploitation of the reservoir.
Downhole formation fluid sampling tools can withdraw samples of fluids from earth formations and transport them to the surface for analysis. The samples are sent to fluid analysis laboratories for analysis of composition and physical properties. There are many inefficiencies inherent in this process.
Only about six samples can be collected on each descent (“trip”) of the tool into the borehole. Because fluid sampling tools are deployed from drilling rigs, and because the rental charge for such rigs can exceed $150,000 per day in the areas where fluid sampling is most often conducted, economic considerations usually preclude multiple trips in the hole. Thus, oil producing formations are almost always undersampled.
Moreover, the samples undergo reversible and irreversible changes as a result of the temperature and/or pressure changes while being brought to the surface and as a result of the transportation process. For example, gases evolve out of solution, waxes precipitate, and asphaltenes chemically recombine. Irreversible changes eliminate the possibility of ever determining actual in situ fluid properties. Reversible changes are deleterious because they occur slowly and therefore impact sample handling and measurement efficiency.
Further, the transportation and handling of fluids uphole entails all the dangers associated with the handling of volatile and flammable fluids at high pressure and temperature. After analyses are complete, the samples must be disposed of in an environmentally acceptable manner, with associated financial and regulatory burdens.
In addition, because fluid analysis laboratories are frequently distant from the well site, there are substantial delays—often several weeks—in obtaining results. If a sample is for some reason corrupted or lost during sampling, transporting, or measurement, there is little possibility of returning to the well to replace it.
No presently deployed system is generally useful for determining the characteristics of sampled formation fluids in-situ while flowing. Accordingly, it is an object of the present invention to provide an apparatus and method which monitors properties while the sample is being taken. It is another object of the present invention to provide an apparatus and method to analyze fluid samples at formation temperature and pressure within the downhole sampling tool.